Settle down a little there fella... Even you admitted that when you dump you never get a smell.
One of two things happened here. Either he isn't dumping in accordance with commonly accepted practice, thus having no smell... or something out of the ordinary happened this one time.
Because you don't mention any unusual dumping procedure, it sounds like something out of the ordinary happened this one time he dumped, causing an offensive odor. How is your neighbor supposed to know that THIS IS THE TIME when its going to smell bad? That's not rude, that's just an unfortunate situation. I'm not sure I have ever seen or head of not being allowed to dump your tanks at a certain time.
If he did something on purpose to offend you, or that he should have reasonably assumed it would offend you... THAT would be rude. Cutting through someone else's site is rude. Blasting music at 11 at night is rude. Dumping your tanks... that's a part of camping.
Like I said... I've never really paid any attention to when I dump my tanks. It doesn't smell bad because I use a proper house and fitting. It is an air tight system (except for the roof black tank vent...). If it is going to bother you that I dump my tanks when they are full, let me apologize now...